posix-cpu-timers: Extend rcu_read_lock removing task_struct references

Now that the code stores of pid references it is no longer necessary
or desirable to take a reference on task_struct in __get_task_for_clock.

Instead extend the scope of rcu_read_lock and remove the reference
counting on struct task_struct entirely.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index b7f972f..91996dd 100644 (file)
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -81,36 +81,36 @@ static struct task_struct *lookup_task(const pid_t pid, bool thread,
 }
 
 static struct task_struct *__get_task_for_clock(const clockid_t clock,
-                                               bool getref, bool gettime)
+                                               bool gettime)
 {
        const bool thread = !!CPUCLOCK_PERTHREAD(clock);
        const pid_t pid = CPUCLOCK_PID(clock);
-       struct task_struct *p;
 
        if (CPUCLOCK_WHICH(clock) >= CPUCLOCK_MAX)
                return NULL;
 
-       rcu_read_lock();
-       p = lookup_task(pid, thread, gettime);
-       if (p && getref)
-               get_task_struct(p);
-       rcu_read_unlock();
-       return p;
+       return lookup_task(pid, thread, gettime);
 }
 
 static inline struct task_struct *get_task_for_clock(const clockid_t clock)
 {
-       return __get_task_for_clock(clock, true, false);
+       return __get_task_for_clock(clock, false);
 }
 
 static inline struct task_struct *get_task_for_clock_get(const clockid_t clock)
 {
-       return __get_task_for_clock(clock, true, true);
+       return __get_task_for_clock(clock, true);
 }
 
 static inline int validate_clock_permissions(const clockid_t clock)
 {
-       return __get_task_for_clock(clock, false, false) ? 0 : -EINVAL;
+       int ret;
+
+       rcu_read_lock();
+       ret = __get_task_for_clock(clock, false) ? 0 : -EINVAL;
+       rcu_read_unlock();
+
+       return ret;
 }
 
 static inline enum pid_type cpu_timer_pid_type(struct k_itimer *timer)
@@ -368,15 +368,18 @@ static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp)
        struct task_struct *tsk;
        u64 t;
 
+       rcu_read_lock();
        tsk = get_task_for_clock_get(clock);
-       if (!tsk)
+       if (!tsk) {
+               rcu_read_unlock();
                return -EINVAL;
+       }
 
        if (CPUCLOCK_PERTHREAD(clock))
                t = cpu_clock_sample(clkid, tsk);
        else
                t = cpu_clock_sample_group(clkid, tsk, false);
-       put_task_struct(tsk);
+       rcu_read_unlock();
 
        *tp = ns_to_timespec64(t);
        return 0;
@@ -389,19 +392,19 @@ static int posix_cpu_clock_get(const clockid_t clock, struct timespec64 *tp)
  */
 static int posix_cpu_timer_create(struct k_itimer *new_timer)
 {
-       struct task_struct *p = get_task_for_clock(new_timer->it_clock);
+       struct task_struct *p;
 
-       if (!p)
+       rcu_read_lock();
+       p = get_task_for_clock(new_timer->it_clock);
+       if (!p) {
+               rcu_read_unlock();
                return -EINVAL;
+       }
 
        new_timer->kclock = &clock_posix_cpu;
        timerqueue_init(&new_timer->it.cpu.node);
        new_timer->it.cpu.pid = get_task_pid(p, cpu_timer_pid_type(new_timer));
-       /*
-        * get_task_for_clock() took a reference on @p. Drop it as the timer
-        * holds a reference on the pid of @p.
-        */
-       put_task_struct(p);
+       rcu_read_unlock();
        return 0;
 }